JPS6148246A - Privacy call device for radiotelephone set - Google Patents

Abstract

PURPOSE:To prevent the generation of a fault due to crosstalk by deciding in advance a setting value of a counter for transmission/reception so as to distinguish the use of the other party. CONSTITUTION:A voice signal of a transmitter 1 is an output (b) subject to digital modulation by a signal subject to N frequency division from an oscillator 2, the signal and an output (a) of a counter 5 set optionally form a meaningless digital code string (c) at an exclusive OR6, and a radio wave 8 subject to FSK modulation is transmitted. The received signal is subject to FSK demodulation, the count of the clock CK is started by an inverted code at counters 14, 15, and a carrier output is obtained only when the count reaches the set count or over, a flip-flip 16 is operated, the original delta modulation is obtained from an output terminal Q and then the voice signal is obtained.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention is applicable to wireless telephone communication, and is intended to be used to prevent interference between telephone devices, eavesdropping on the contents of another person's call, and communication using another person's telephone number. It concerns preventive measures.

Conventional configurations and their problems Conventionally, the main countermeasures of this type have been to change the communication frequency to prevent interference with other people and to prohibit the use of other people.

However, with the conventional method, it is possible for someone else to easily match this communication frequency, and it is not a definitive method of confidential communication, but it also causes abnormal noise due to interference from nearby users, making it loud on the call. This was a problem.

OBJECT OF THE INVENTION The object of the present invention is to eliminate such conventional problems, even if
Even if the used frequencies match, no signal can be obtained, and it can prevent eavesdropping and stealing by others, and even if it is used.

To provide a secret communication device for a wireless telephone, which avoids generation of abnormal noise due to conventional interference and provides clear communication since dial information, voice of a call, etc. cannot be heard.

Structure of the Invention The present invention is based on the principle of converting a signal obtained by delta modulation and a clock frequency for delta modulation into a meaningless digital code system by obtaining an exclusive OR. The principle is that the exclusive OR of the digital code system thus obtained and the above-mentioned clock frequency is performed again to obtain a delta modulated signal, which is then passed through an integrator to obtain a voice signal.

If the system clock frequency is changed to the same value using a counter or the like, the same demodulation will be performed, but if the clock frequencies for transmission and reception are different, a pseudo-random digital code system will result, and the demodulated signal will be silent. Furthermore, when transmitting as radio waves, by changing the value of the two frequencies of FSK (frequency shift modulation in which the digital 0 value is fl and the 1 value is f2), a more complicated secret communication device can be provided.
Even if interference occurs from nearby users, the output will be silent and the generation of conventional abnormal noises can be avoided.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an embodiment of a wireless telephone secret device according to the present invention. In Figure 1, 1 is a transmitter, 2 is an oscillator such as a crystal oscillation, 3 is a 1/N frequency divider, and 4 is a delta modulator (P
DM), 5 is a counter that can be set as desired, 6
is an exclusive OR circuit, 7.11 is an FSK modulator, 8 is an out-of-band frequency removal filter, 9.10 is a transmitting/receiving antenna, 12 is a buffer, 13 is an inverter, and 14.15 is a transmitter. 16 is a flip-flop (
F/F), 17 is a resistor, and 18 is a capacitor. In such a configuration, the voice signal of the transmitter 1 is delta-modulated by the N-divided signal from the oscillator 2 and output, and is further output from the arbitrarily set output a of the counter 5 and the exclusive OR circuit 6. A meaningless digital code string C is obtained, FSK modulated by an FSK modulator 7, and transmitted as a radio wave 8 from an antenna 9. Here, the radio wave 8 is received by a receiving antenna 10 on the handset or main body side, demodulated into FSK by an FSK demodulator 11, and one side is connected to an inverter 13 via a buffer 12, and the other side is directly connected to a counter 15. Here each counter 14
, 15, starts counting the clock CK with the opposite sign, and outputs a carry output only when the count exceeds the set value, operates the cent and reset terminals S and R of the flip-flop 16, and sends it to the output terminal Q6. A delta modulated output of the original is obtained, and an audio signal is obtained from the terminal q from an integrating circuit consisting of a resistor 17 and a capacitor 18.

Furthermore, a timing chart of each part is shown in FIG. The correct delta modulation signal S becomes the signals c and d by exclusive ORing with the signal a, and even if it is demodulated as it is via an integrator, the pseudo-random output signal will be silent.

Therefore, in the receiver system, the counter is configured to count in the opposite direction so that the counter operation time is output on the rising edge and the falling edge, respectively, and a carry is output for input exceeding the set count value to calculate the delta. It demodulates the modulation.

In other words, it can be seen that the system works well even without synchronization between the transmitter and receiver.

e is the output of the counter 16, f is the output signal of the counter 14, and q is the demodulated signal of the secret signal.

Effects of the Invention As described above, according to the present invention, it is possible to prevent 7-vehicle interference by nearby users, eavesdropping from others, and theft.
This is not possible by changing the transmitting and receiving frequency of K, but by setting the transmitting and receiving counter settings in advance, it is possible to differentiate the use from others, and the dial tone signal can also be set using the same method. Because it can be
Confidential communication using a wireless telephone can be realized at a low cost, and since the confidential communication is muted against eavesdropping by others, it has a great effect in that others do not notice.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a wireless telephone secret device according to an embodiment of the present invention, and FIG. 2 is a timing chart of each part of FIG. 1. 1... Transmitter, 2... Oscillator, 3...
...Frequency divider, 4...Delta modulator, 5,14
．． 16... Counter, 6... Exclusive OR circuit, 7... FSK modulator, 9, 10...
...Antenna, 11...FSK demodulator, 16
····flip flop.

Claims (2)

[Claims] (1) A radio telephone transmitting system having a delta modulator, a first counter, an exclusive logic element, and an FSK modulator; and a receiving system having an FSK receiver, a second counter, and a delta demodulator; In the transmitting system, the output of the arbitrarily set first counter and the output of the delta modulator are applied to the exclusive logic element to perform FSK modulation on the output signal, and in the receiving system, the output signal is FSK-modulated.
The K-modulated signal is demodulated, and this demodulated signal is converted into a second
A secret communication device for a wireless telephone consisting of inputting an input to a counter and inputting its output to a delta demodulator. (2) A delta modulator that performs delta modulation on the audio signal input from the transmitter, a frequency divider that divides the clock signal that controls the entire device by N, and a divided output signal of the frequency divider. It has a first counter that can be set arbitrarily and an exclusive OR circuit, the output of the delta modulator and the output signal of the counter are input to the input terminal of the exclusive OR circuit, and the exclusive OR circuit The second counter has a transmission system which applies FSK modulation of two or more frequencies to the output of the transmission system, and a second counter that can arbitrarily set a count value for the output of the transmission system in two opposite directions. It consists of a reception system that receives signals by demodulating the output of the counter, and by setting the count setting value of the transmission system and the count value of the reception system the same, the voice signal of the transmitter is obtained, and the other settings 2. The wireless telephone secret communication device according to claim 1, wherein a meaningless signal is obtained when the wireless telephone is used.